The 1999 Gordon Research Conference (GRC) on Molecular Concepts in Radiation Oncology will be held at the Holiday Inn, Ventura, California, January 31- February 5, 1999. This is the second conference related to this topic with the first, in June 1997, being very well received. This proposal is for partial support for travel and expenses for invited participants. There continues to be extraordinarily rapid progress in understanding the response of the cell to ionizing radiation (IR) including: identifying the molecules involved in DNA damage recognition and repair, the role of signal transduction pathways that are activated by damage to DNA and other macromolecules including the cell membrane, and the role of the molecules used by the cell to delay cell cycle progression and initiate apoptosis. The molecular processes involved in genomic instability and tumor microenvironmental effects, including the stress response, are also being elucidated. The knowledge of the molecular response to IR is enhancing the understanding normal tissue injury and is leading to the development of novel therapeutic approaches in the clinic. The GRC will bring together basic, translational and clinical scientists to discuss these new developments and to explore their potential for advances in cancer treatment by radiation oncology.